Value of physical and pharmacological tests in predicting intrinsic and extrinsic sick sinus syndrome

We studied 13 patients with sick sinus syndrome using various physical (postural reflex testing. Valsalva manoeuvre, carotid sinus massage), pharmacological (intravenous isoprenaline, atropine, neostigmine and total autonomic blockade) and electrophysiological tests in order to identify simple non-invasive markers of intrinsic sick sinus syndrome. Following autonomic blockade, 6 patients had normal and the remaining 7 had an abnormal intrinsic heart rate. Electrophysiological testing revealed abnormal sinus node parameters in 8 (62%) subjects in the basal state and 11 (85%) after autonomic blockade. Carotid sinus massage was abnormal in all patients (100%) with an abnormal intrinsic heart rate, and in only 2 of the 6 (33%) with normal intrinsic heart rate (P less than 0.05). The heart rate response to isoprenaline was abnormal in 5 of the 6 (83%) patients with normal as compared to only 1 of the 7 with abnormal intrinsic heart rate. With isoprenaline there was a significantly (P less than 0.05) higher increase in heart rate in patients with abnormal as compared to those with normal intrinsic heart rate. The other physical and drug tests were not helpful to differentiate between intrinsic and extrinsic mechanisms. Thus, carotid sinus massage and, to some extent, isoprenaline administration appear simple bedside tests which may be helpful in identifying the underlying mechanism of sick sinus syndrome.